The use of plated plastic in antenna systems and waveguides is expanding due to several advantages that plated plastic offers, such as:
- Lighter weight compared to aluminum and other metals, which is especially important in many applications, especially in aircraft and space based systems.
- More complex design that can be achieved with injection molded plastic compared to machined metal parts.
- Lower cost in volume production – injection molded plastic can offer significant cost reductions versus machined aluminum or other metals. Additionally, injection molded plastics can be produced in much higher volumes than machined metal waveguides. Injection molded and plated plastic waveguides can be competitive with die cast metal components in many applications.
Once the plastic waveguide is fabricated, it needs to be plated to provide the conductive surface required for the antenna function. The plating thickness is typically 4-10 µm depending upon the antenna frequency band. Most often the plating metal is copper due to its high conductivity and relatively low cost. The copper plating is deposited by a process known as electroless plating. No pre-plating conductive layer is required. The copper plating is deposited directly onto the plastic waveguide. The plating adhesion can be equivalent or even superior to the adhesion of circuit traces on epoxy glass PC board. Also, one of the advantages of electroless plating is that it deposits a uniform thickness metal layer over the entire surface of the waveguide, which can be critical to antenna performance.
There is a wide range of plastic resins that can be plated, including ABS, Polycarbonate (PC), PC/ABS, Polyetherimide (PEI), Liquid Crystal Polymer (LCP), Polyetheretherketone (PEEK), Fiberglass, PA/PPA/nylon polyphenylene ether (PPE), and polystyrene to name a few options. Consult Cybershield for optimal resin selection for your waveguide application.
A key issue for many designers is how to protect the copper plating from oxidation in use. This can be accomplished in one of several ways, including.
- Plating a thin layer of electroless nickel over the copper if your antenna can allow thin layer of magnetic material. If it cannot, there are still options.
- Electroless nickel is comprised of nickel and phosphorous. When the phosphorous content is above 11% it becomes non-magnetic. This plating is call high phosphorous electroless nickel.
- Silver can be electroplated over copper to provide improved corrosion protection. The cost of silver plating can impact final cost for the plated plastic waveguide.
- Passivation can significantly improve corrosion resistance of copper plating. This is a process where the copper plated waveguides are immersed in a tank that includes Benzotriazole, which forms a microscopic barrier layer on the copper plating surface. This forms an effective corrosion inhibitor. This microscopic layer is extremely low in cost and does not impact the surface conductivity of the copper plating. Passivated copper plated waveguides have been in use in outdoor applications for over 10 years with continued excellent performance.
The selection of the layer to protect the copper plating should be evaluated by the customer in its end use environment to determine the most cost effective system that meets the corrosion and durability requirements.
In summary, plated plastic waveguides can provide significant advantages over machined and even die cast alternatives. Cybershield Applications Specialists can work with you to determine if your waveguide is a good fit for plated plastics.